1. Field of the Invention
The present invention relates to a valve for an internal combustion engine and, more particularly, to a cylindrical rotary valve having two transverse parallel passageways.
2. Description of Related Art
Inherent to the operation of a reciprocating internal combustion engine is the requirement that it have a valve or valves for reliably communicating a mixture of fuel and air into the engine cylinders and for subsequently exhausting the products of combustion. A concomitant requirement is that such valves open and close during the appropriate periods in the operation cycle. The valves must also provide for a tight seal when they are in a closed position.
The common approach to the valve requirements of the reciprocating internal combustion engine is the use of one or more spring-loaded tulip-shaped valve structures formed from metal. Each valve head seats tightly into a tapered opening, or port, in the head wall of the engine cylinder to seal the cylinder. This requires that the valve head have a very precise shape, with low tolerance for deviation from the design specification.
The valve includes an elongated stem which moves reciprocally in a guide, which is comprised of a bore in the cylinder head. A spring fits around the valve stem and is attached to the top of the stem. The spring is in compression and exerts an axial force which, in the absence of an opposing axial force on the end of the valve stem, is sufficient to keep the valve seated.
The end of the valve stem abuts one end of a pivoting rocker arm. The other end of the rocker arm abuts the end of a push rod. The push rod is reciprocally moved axially by a solid lifter which rides on a cam lobe on a camshaft. The camshaft is rotated by the engine crankshaft by means of a reduction gear or a gear and chain arrangement. Rotation of the crankshaft is thereby mechanically translated into an axial force on the valve stem which opposes the spring force. The force translated through a push rod when the lifter is riding on the high point of a lobe on the camshaft is sufficient to overcome the spring force and unseat the valve by pushing it into the cylinder.
This type of intake and exhaust valve has been widely adopted as the solution for the valving requirements of the internal combustion engine primarily because of the relative ease by which adjustments can be made for wear, reasonable manufacturing costs, and the proven reliability of the design. However, as hereinafter detailed, the intrinsic disadvantages of such valves and the necessary compromises in engine performance occasioned by their use are numerous.
The mechanical linkage which connects the valve to the crankshaft is noisy and subject to wear due to friction between the numerous moving parts. The wear decreases key part dimensions and thereby causes the valve to open later and close earlier than the design specifications, a conditions known as "valve lag." This decreases the period the valve remains open, deleteriously affecting engine efficiency and performance.
Furthermore, the harsh operational environment of the valve and the assorted mechanical parts necessary to drive it through its reciprocating motion requires that they be formed from durable metal that retains its strength at high temperatures, and thus has a high density which results in each of the parts having a relatively high mass. As the valve and its associated parts are in motion during every combustion cycle, their high masses give rise to inertial forces which can cause the movement of the valve to lag behind its design parameters, especially at high rates of crankshaft revolution.
In addition, at very high rates of crankshaft revolution the valve spring force is ofttimes not sufficient to completely seat the valve head before the beginning of the subsequent engine cycle, a condition known as "valve float." In such a situation, damage to the valve, cylinder wall or piston can result from the piston striking the unseated or "floating" valve head. This problem can be overcome to some extent by increasing the spring force, but this remedy adds greatly to the wear on the valve actuating mechanism and may also cause bending or fracture of the push rod.
The noise of the conventional intake and exhaust valve and the wear and concomitant adjustment requirements can be reduced by replacing the solid lifters with hydraulic lifters. However, such a modification aggravates the problem of valve float.
Another approach to the long-standing problem of valve lag is to locate the camshaft above or adjacent to the intake and exhaust valves and place the end of the valve stem in direct contact with the camshaft lobe or rocker arm. This eliminates the need for a lifter, a push rod, and possibly a rocker arm, and thus reduces the mass and the inertia of the valve mechanism. However, although improving the performance of the valve at high rates of crankshaft revolution, the increased distance between the camshaft and the crankshaft relative the the conventional camshaft location requires a more complex mechanism to maintain the necessary revolution ratio between the camshaft and the crankshaft. This increase in complexity increases the cost of the valve mechanism.
As the conventional valve is seated in a port in the head wall of the cylinder, its diameter is limited by the diameter of the bore of the cylinder. The valve diameter, in turn, limits the flow rate of the mixture of air and fuel that can be drawn into the cylinder, as well as the flow rate of combustion products exhausted out of the cylinder. The more of the combustible mixture that can be drawn into the cylinder during the charging interval of the combustion cycle, the more power the engine can produce during the combustion cycle. The quotient of power divided by the volume of the cylinders is known as the volumetric efficiency of the engine.
The valve diameter also directly affects the work required of the reciprocating piston to draw the combustible mixture into the cylinder and exhaust the products of combustion from the cylinder, a parasitic power loss known as the "pumping loss." The larger the valve diameter, the lower the "pumping loss."
Use of the conventional intake and exhaust valve has obliged engineers to increase bore diameter of the cylinder in order to increase the valve diameter and realize the attendant power gains, albeit ofttimes at the sacrifice of other performance parameters. Another means of increasing volumetric efficiency is to increase the number of valves, while making them smaller in diameter. Although this approach will improve volumetric efficiency, the increased complexity and miniaturization of the valve mechanism increases its cost of manufacture and repair.
The face of the conventional exhaust valve is repeatedly inserted into the cylinder immediately after combustion when the cylinder contains the hot gaseous products of combustion. It thus becomes red hot and promotes preignition of the fuel charge. Preignition limits the compression ratio of the cylinder and its suppression may require increasing the octane rating of the fuel. The power output of an engine is directly related to the compression ratio of its cylinders.
In summary, the limitations of the conventional intake and exhaust valve used in internal combustion engines arise from its inherent sensitivity to fit when it is seated, as well as to the amount of time it is seated and, alternatively, open. As these parameters are directly affected by the mass and wear of the numerous moving parts in the linkage connecting the valve to the crankshaft, there is a limit to the valve's performance and reliability. The volumetric efficiency of an engine cylinder serviced by the valve is also limited. Further, the valve subjects the engine cylinder to preignition. Although there are modifications to the basic design which can improve various aspects of the valve's performance, any of these improvements come at the expense of reliability and other performance parameters.
There have been a number of rotary valve designs prompted by the aforementioned limitations inherent to the conventional valve. One approach is to situate one cylindrical sleeve concentrically within another. Both sleeves have ports and rotate relative to each other. Fluid communication with the engine cylinder is obtained when ports in both sleeves overlap or register with one another. Rotary valves of this type are shown in U.S. Pat. No. 1,299,264 issued to Thayer, U.S. Pat. No. 1,378,092 issued to Carmody, and U.S. Pat. No. 3,060,915 issued to Cole. Cole passes the fuel mixture axially through the hollow inner sleeve of an intake valve, and exhausts the products of combustion axially through the hollow inner sleeve of a parallel exhaust valve.
Another type of rotary valve uses a shaft having transverse passageways which alternatively communicate fuel and exhaust as it rotates. Examples of this type are shown in U.S. Pat. No. 3,990,427 issued to Cross et al, and U.S. Pat. No. 4,342,294 issued to Hopkins. Cross passes the fuel mixture and the exhaust gases through separate passageways running axially through the shaft.